$ { {5} \times \left[\begin{array}{rr}{2} & {4} \\ {-1} & {-2}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{5}\times{2} & {5}\times{4} \\ {5}\times{-1} & {5}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{10} & {20} \\ {-5} & {-10}\end{array}\right]}$